According to the passage, the numerical value of the concentration level of a substance

Câu hỏi :

According to the passage, the numerical value of the concentration level of a substance is only useful if __________. 


A. it is in a localized area                                      


B. the other substances in the area are known

C. it can be calculated quickly                          

D. the natural level is also known 

* Đáp án

* Hướng dẫn giải

Chọn đáp án D

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